Electronic ovens heat items within a chamber by bombarding them with electromagnetic radiation. In the case of microwave ovens, the radiation most often takes the form of microwaves at a frequency of either 2.45 GHz or 915 MHz. The wavelength of these forms of radiation are 12 cm and 32.8 cm respectively. The waves within the microwave oven reflect within the chamber and cause standing waves. Standing waves are caused by two waves that are in phase and traveling in opposite directions. The combined effect of the two waves is the creation of antinodes and nodes. The waves perfectly interfere at the nodes to create spots where no energy is delivered. The waves perfectly cohere at the antinodes to create spots where twice the energy of a single wave is delivered. The wavelength of the radiation is appreciable compared to the speed at which heat diffuses within an item that is being heated. As a result, electronic ovens tend to heat food unevenly compared to traditional methods.
Electronic ovens are also prone to heat food unevenly because of the mechanism by which they introduce heat to a specific volume of the item being heated. The electromagnetic waves in a microwave oven cause polarized molecules, such as water, to rotate back and forth, thereby delivering energy to the item in the form of kinetic energy. As such, pure water is heated quite effectively in a microwave, but items that do not include polarized molecules will not be as efficiently heated. This compounds the problem of uneven heating because different portions of a single item may be heated to high temperatures while other portions are not. For example, the interior of a jelly doughnut with its high sucrose content will get extremely hot while the exterior dough does not.
Traditional methods for dealing with uneven cooking in electronic ovens include moving the item that is being heated on a rotating tray and interrupting the beam of electromagnetic energy with a rotating stirrer. Both of these approaches prevent the application of an antinode of the electromagnetic waves from being applied to a specific spot on the item which would thereby prevent uneven heating. However, both approaches are essentially random in their treatment of the relative location of an antinode and the item itself. They also do not address the issue of specific items being heated unevenly in the microwave. In these approaches, the heat applied to the chamber is not adjusted based on the location, or specific internal characteristics, of the item being heated.